Amman, Jordan — In a major address to the Muslim world from Cairo on June 4, President Obama is expected to unveil his peace plan for the Arab-Israeli conflict.

While the details have yet to emerge, and numerous challenges remain, many Arab leaders see a window of opportunity to end the conflict after more than half a century.

"The level of optimism is pretty significant. We haven't seen this for a long time," says Mohammad al-Momani, a political science professor at Yarmouk University in Irbid, Jordan. "People believe that Obama understands that there is a need for concrete action on the Arab-Israeli conflict and that he has shown ... significant commitment to [resolving] the conflict."

One of the most prominent Arab leaders seizing this moment has been Jordan's King Abdullah II. While Egypt and Saudi Arabia – whose contacts and wealth have long made them influential – will likely preserve their traditional roles, the king is emerging as the unofficial spokesman for peace, forging ties in both the Middle East and the West.

He was the first Arab leader invited by Mr. Obama to the Oval Office. He hosted Pope Benedict XVI (who reiterated calls for a Palestinian homeland), shuttled between leaders from Europe to Japan, worked to reconcile rifts within the Arab world, and received Israeli premier Benjamin Netanyahu.

"He is really the prime mover of the cause of peace in the region," says Abdel-Elah al-Khateeb, a former Jordanian foreign minister. "He has the credibility, the stamina, the determination, and the conviction to do it. This is not an easy task in a region where radicalization is taking deep root because of the failure to achieve peace between the Israelis and Palestinians."

With only 6.3 million people – one-third of Cairo's population – and almost no resources, Jordan may seem an unlikely state to carry much diplomatic weight. Yet as the second Arab state to normalize relations with Israel and the only one to border the West Bank, it has historically played a significant role in the peace process. Nearly 60 percent of Jordan's population is Palestinian. As many Jordanians say, Palestine's problems are Jordan's problems.

Educated in the United States and at Britain's Sandhurst military academy, the king relates easily to Westerners. Yet he also has the trust of moderate Arab leaders. In May, he lobbied on their behalf for US support of the Arab Peace Initiative. Drafted by Saudi Arabia in 2002, the plan states that Arab nations will recognize Israel in exchange for Israel withdrawing from the West Bank and Gaza and resolving the status of more than 4.5 million Palestinian refugees.

King Abdullah has proposed a "57-state solution" that would expand that initiative to include non-Arab Muslim states as well. Whereas the divided Palestinians are struggling to speak with one voice and can offer Israel little in return for any concessions, having the Arab world at the table could change that calculus significantly.

"Who's going to give Netanyahu the incentive he needs to make concessions? It's going to have to come from the Arab states," says Tamara Wittes, a Middle East expert at the centrist Brookings Institution think tank in Washington. "The activism of Egypt and Jordan is important not just in changing the tone, but also in corraling the rest of the Arab world into taking the necessary steps to support the peace process."

In the end, the king is unlikely to eclipse Saudi Arabia's traditional leadership role, says Mr. Aaron. "He has the other King Abdullah [of Saudi Arabia] to deal with, who has actually made great strides in putting forward his own proposal and getting it adopted by the Arab League," he says, "but it's possible he could be in a meditating role."

KING ABDULLAH HAS STRESSED that time is short; if a comprehensive solution is not reached quickly, he warned in May, war could break out within 18 months.

"In the last 15 years, to a great extent all issues have been overnegotiated, so it's time for decisions. It's time to show political will," says Mr. Khateeb.

However, Abdullah and his allies may find it more challenging to execute a peace deal than their predecessors in Oslo and Madrid. In the early 1990s, the Israelis were more receptive to peace and Palestinians were unified under Yasser Arafat.

Mr. Netanyahu, known as uncompromising during his 1996-99 term, has not supported Palestinian statehood. But in his visit with Obama May 18 he said he "shared" the urgency expressed by King Abdullah. It's likely the US will pressure him to prove that commitment, says Jordanian parliamentarian Fayez Tarawneh, a former prime minister. Given the new Obama administration, the financial crisis, and the rise of the Iranian threat, he says, "I don't think the Americans will leave Israel ... the luxury of dictating everything in the Levant."